Protective Responses of Green Yuja Peel Extracts to Lipopolysaccharide-Induced Inflammation and Reactive Oxygen Species Production in RAW264.7 Cells

This study assessed the anti-inflammatory and antioxidant effects of green yuja peel hot water extract (GYW) and ethanol extract (GYE) on lipopolysaccharide (LPS)-stimulated RAW264.7 cells. GYW and GYE (50, 100, and 200 μg/mL) significantly reduced the LPS-induced production of nitric oxide (NO), interleukin (IL)-6, tumor necrosis factor-α (TNF-α), and reactive oxygen species in a concentration-dependent manner, without cytotoxicity. Compared with control cells, GYW and GYE significantly downregulated the protein levels of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) and the gene expression of <i>iNOS</i>, <i>COX-2</i>, <i>TNF-α</i>, and <i>IL-6</i>. Conversely, they upregulated the gene expression of <i>IL-10</i>. Moreover, GYW and GYE significantly suppressed NF-κB p65 and IκB-α phosphorylation and increased the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream target heme oxygenase-1 (HO-1) compared with control cells. These results suggest that GYW and GYE exhibit anti-inflammatory and antioxidative properties by downregulating the NF-κB signaling pathway and upregulating the Nrf2/HO-1 system in LPS-activated macrophages.